Environmental and Molecular Mutagenesis - Legacy Tobacco ...

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METABOLISM AND ACTIVATION OF FOOD MUTAGENS
N .J . Gooderham, B.P. Murray, S. Murray, A .R . Boobis and D.S. Davies. Department of Clinical Pharmacology,
Royal Postgraduate Medical School, London, W12 ONN, UK .
There is considerable evidence that diet plays a major role in the aetiology of cancer in man . In addition
to naturally occurring carcinogens present in food, a number of heteroaromatic amine carcinogens are known
to be formed during the cooking process . These include imidazoquinoline/ lmidazoquinoxaline (IQ
compounds) which are of particular interest due to their high mutagenic potency . Consumption of cooked be te
containing the IQ compound 2-amino-3,8-dimethytitnidazo[4,5-fiquinoxaline (MeIQx) at levels of 0 .8 -
2 .sng/g beef, resulted in systemic exposure, evidenced by urinary excretion of 1 .3 - 4 .9% of the dose as
unchanged amine . Studies in animals have shown that MelQx is almost completely absorbed but then undergoes
extensive metaboli m, with only small amounts of unchanged amine excreted in urine . After administration
(oral, ip or iv) of [i4C)Me1Qx (2 - 60mg/kg) to mice, 25 - 35% of radioactivity was excreted In urine and a
further 35-45% was eliminated in faeces within 24 h . Urinary metabolites of MelQx included N-acetylsted,
N-sulphated, N-glucuronidated, ring N2-demethylated, C8-hydroxylated and ring CS-hydroxylated
derivatives . IQ compounds are readily activated by liver microsomal fractions to derivatives which are
genotoxic in the Ames Salmonella typhimurium test . Human liver microsomes are particularly efficient at
activating these amines. The primary activated product of microsomal oxidation is thought to be the exocyclic
amino N-hydroxy derivative . Studies of hepatic microsomal activation of IQ compounds, employing
monoclonal antibodies and specific chemical inhibitors, have shown that they are converted to mutagenic
derivatives by a monooxygenase system predominantly involving the cytochrome P-450 isozyme orthologous
to rat P-450d .
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MUfAL2I1S IN 1QNYAN '1RADITIQiAI. MICIId: PtEC3IIATiQS .
H .N.B . Copalan and A.N . WairimA, University of Nairobi, Department of Botany, P .O. Haet 30197, Nairobi
(Kenya)
Several plant praducts are used in Kenyan traditianal medicine which is popular both in rural and
urban centres . 7his form of inedicine is gaining raamenum due to goverrnrntal support and active
interest in it from both physicians acd pharmacologists . Several of the plant producta are in camen
usage . Houever, their effects have not been vigorausly tested . In the current study, the fresh sap fram
Aloe graminicola, ard the sethanol extrazts of Amona aenegelensia, Centella asiatica, Msess lanceolat :a,
sine africana ~d I rica salisifolia Which are all extensively used in Benyat tr~aditional medicine,
were tested for their garotoxicity using the Nmes test and the Vicia faba root meristem assay . TA 104
yielded the highest nuaaer of revertants vith soet extracts . TA 102 detected aame but not as
effectively as TA 104 . A reduction in nuober of revertants at higher does uas noticed . Apart from
M. lanceolata, all other plant extracts induced abrotael metaphaaes in V . faba root taeristem cells,
after 2 hrs of treatrrent . After recovery, only the extracta from C.aas'iatTc-a-, M . africata and
M . salisifolia caused statistically significant increase in chromosoae aberrations . Fcesh extract of
A . graminicola induced micracuclei formation after recovery . 'ilau several plants used in itenyan
craditional medicine appear to erfiibit m¢agatic potential . Further atudies using pirified etaaacts
are needed before recanendations regarding eotuinued use can be made•
* lbrk foras part of the requirarents for the degree of Master of Science of the University of
Nairobi .
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A FORWARD Ml1TATIONAL SYSTEM TO DF.TECT FRAMESHIFTS WIT1i1N A IRO BASB-PA1R TARdI:T
OF F.schcrichia cnlr. Alasdair J.F C)ordon, Jennifer A. Halliday, Michael J . Horsfall and Barry W .
Olickman . Dept. of Biology, York University Toronto Canada M3J 1P3 .
A forward mutational system is described which is based on the acquisition of lacl negative
dominant properties as the resolt of secondary frameshift mutation (of either sign) within that region of
the lacl gene that encodes the DNA-binding domain of the lac repressor . Strains containing both I'd
(dominant-negative) and wild-type alleles of the lacl gene exhibit constitutive synthesis of Qgalactosidase
and thereby grow on agar plates in which the non-Inducing sugar phenyl-i3•D-galaetoaide is
the sole carbon source . A consequence of -1 frameshifts in the initial 180 base-pain of lacl is the inframe
creation of translation termination signals. Translation reinitiation at codons Va123, Met42 or
Leu62, results in repressor fragments that confer the 1'd phenotype since the ability to aggregate fa
function of the core domain) is not impaired . However, the first in-frame stop codon which results from
a+ I frameshift is at buse-pair 277 t1legl/Lyag4Y and therefore translational reinitiation will not produce
the intact core domain required for an 1'd phenotype . Utilising an F7acl factor with a +A frameshift at
position 46 (recessive negative) we have devised a test which specifically selects irattteahifts as events
that yield the I-d phenotype. Within the 181) base-pair target frameahifts of rither sign 1+ I or -1) cnn be
detected ; -1 events restore the reading frame of the core domain ; +1 events in conjunction with +A46
exhinit the con.equences of a-1 frameshift. In either aae, some portion of the DNA-hinding domain will
be non-functional and hence the repressor will be 1-d . This selection system In combination with routine
cloning and sequencing technologies will facilitate the rapid colliection and characterisation of the large
numbers of mutations required for studies of mutational specificity .
http://legacy.library.ucsf.edu/tid/clb93d00/pdf
1989 EMS Abstracts
Notes
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